Protective filter lens

ABSTRACT

An ophthalmic, protective, filter lens, and a method of producing such lens, the lens having a ratio of Z and Y tristimulus values between 0.25-0.40, a dominant wavelength between 570-580 nm. on a color mixture diagram, a sharp transmission drop between 450-500 nm. and a transmission not over 30% between 400-450 nm.

This application claims the benefit of U. S. Provisional Application,Ser. No. 60/099,534, filed Sep. 9, 1998, entitled PROTECTIVE FILTERLENS, by T. G. Havens, D. J. Kerko and B. M. Wedding, and SupplementalProvisional Application, Ser. No. 60/107,380, filed Nov. 6, 1998,entitled PROTECTIVE FILTER LENS, by T. G. Havens, D. J. Kerko and B. M.Wedding.

FIELD OF THE INVENTION

A photochromic filter lens having a reduced surface layer to controlspectral transmission and method of making.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 4,284,686 (Wedding) describes a series of ophthalmicfilter lenses and their production. These lenses are specially designedto alleviate the discomfort experienced in bright light by individualsafflicted with certain visual deficiencies.

All of the commercially important photochromic glasses are glasses whichcontain a precipitated, microcrystalline, silver halide phase. It isthis phase which is considered to cause the reversible darkening of theglass upon exposure to light. U.S. Pat. No. 3,208,860 (Armistead et al.)provides the basic description of this family of glasses. Subsequentwork has resulted in the development of many new families ofphotochromic glasses exhibiting faster darkening and/or fading response.U.S. Pat. No. 4,190,451 (Hares et al.), for example, provides adescription of some recently developed photochromic glasses of thistype.

The patent discloses glasses which are particularly suitable for use inthe inventive method. Such glasses consist essentially, expressed inweight percent on the oxide bases, of about 0-2.5% Li₂O, 0-9% Na₂O,0-17% K₂O, 0-6% Cs₂O, 8-20% Li₂O+Na₂O+K₂O+Cs₂O, 14-23% B₂O₃, 5-25%Al₂O₃, 0-25% P₂O₅, 20-65% SiO₂, 0.004-0.02% CuO, 0.15-0.3% Ag, 0.1-0.25%Cl, and 0.1-0.2% Br, wherein the molar ratio of alkali metal oxides:B₂O₃varies between about 0.55-0.85 and the weight ratio Ag:(Cl+Br) rangesbetween about 0.65-0.95. Those glasses may also optionally contain up toabout 10% total of other ingredients selected from the group in theindicated proportions of 0-6% ZrO₂, 0-3% TiO₂, 0-0.5% PbO, 0-7% BaO,0-4% CaO, 0-3% MgO, 0-6% Nb₂O₅, 0-4% La₂O₃ and 0-2% F. Finally, thosecompositions are compatible with the conventional glass colorantsselected from the transition metal oxides and rare earth metal oxides.Hence, up to about 1% total of transition metal oxide colorants and/orup to 5% total of rare earth metal oxide colorants may be included tomodify the color of the bulk glass.

Colored, ophthalmic lenses, developed in accordance with the Weddingpatent teachings, have provided relief for patients having light orglare sensitivity problems. Dye-impregnated, plastic lenses have beendeveloped as alternatives. The latter are sometimes referred to as“blockers” since they are stated to absorb all of the light below acertain wavelength.

A major problem with the “blocker” lens is that total absorption of partof the spectrum greatly distorts color perception. This may also occurin the surface colored, glass lens with an unduly long treating time.However, the time of the reducing treatment may be adjusted so that acarefully controlled, small amount of blue transmission, referred to asa “blue leak,” occurs. This provides a less severe distortion of colorperception.

Nevertheless, it would be desirable to further improve natural colorperception in a protective filter lens.

Subsequent developments have enabled the filter lenses disclosed in theWedding—686 patent to be produced with much shorter firing times. Forexample, a filter lens, having its cutoff over a wavelength range ofabout 450-500 nm. in the visible, can be produced by firing the lens inflowing hydrogen for two hours at about 476° C.

However, it is still necessary to “front surface” the lens after firing.This involves removing the reduced glass from the front surface of thelens. This is necessary to permit access of actinic radiation to darkenthe photochromic glass. Further, if a fused, multifocal lens is to beproduced, it is necessary to remove the reduced layer in order to fusethe segment in place.

One object of the present invention is to obviate the need for the frontsurfacing procedure.

Another object is to provide a protective filter lens that closelyapproximates transmission of a natural color scene, that is, allows aviewer to see the actual, undistorted colors in a scene.

A further object is to provide these features either in a lens that isuntinted, or in one that has a fixed tint imparted to the glass.

It is also an object to reduce the time factor in the process withoutimpairing the effectiveness of the lens.

Another object is to enable processing of photochromic, progressivelenses.

SUMMARY OF THE INVENTION

The invention resides, in part, in an ophthalmic, protective, filterlens having a ratio of Z/Y tristimulus values between 0.25-0.40, adominant wavelength between 570-580 nm. on a color mixture diagram, asharp transmission drop between 450-500 nm., and transmission not over30% between 400-450 nm.

The invention further resides in a method of producing an ophthalmic,protective filter lens which comprises firing a silverhalide-containing, photochromic glass lens in a hydrogen-containingatmosphere within a temperature range of 465° C. to 495° C. for a timeless than 20 minutes, but sufficiently long enough to provide Z/Ytristimulus values in the lens such that the ratio of Z/Y is between0.25-0.40.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings,

FIG. 1 is a graphical representation of transmittance data comparing aconventional, commercial lens with a lens in accordance with the presentinvention.

FIG. 2 is a graphical representation in which the Z/Y ratio for severaldifferent lenses and Illuminants are plotted against spectral purity.

FIG. 3 is a graphical representation in which the relative luminousefficiencies for the three types of cone photoreceptors are plottedagainst wavelengths of visible light.

BRIEF DESCRIPTION OF THE INVENTION

Several, different protective filter lenses have been developed based onthe Wedding—686 patent teaching. One of these, known under thedesignation, CPF 450, is designed to provide spectral transmissioncutoff between 500-450 nm. This lens has proven technically effectivefor its purpose. The present invention, however, is based on studiesdirected at improving the natural color perception of this lens, as wellas simplifying its production.

As noted above, studies have shown that the blue end of the spectrum,that is, wavelengths below about 500 nm., is very important indetermining natural color perception. Thus, as noted, total blocking oftransmission in this region, as with a “blocker” lens, provides serious,color scene distortion. Transmission at the lower wavelengths, that is,at the blue end of the visible spectrum, is much less than at longerwavelengths. Nevertheless, its significance is much greater indetermining proximity to natural color perception.

Earlier studies have defined filter lenses in terms of dominantwavelength and color purity with respect to a region in a 1931 CIE colormixture diagram. In such diagram, color data are plotted in terms of xand y values on their respective axes. The values are then computed bythe weighted ordinate method using 1931 Illuminant C and the CIEStandard Observer.

The values may be compared to either Illuminant C, a value defined interms of light from a northern sky, or Illuminant A, a value determinedby the spectral distribution from a tungsten lamp. The latter iscommonly considered to be a white light.

Our present studies show that the ratio of the Z tristimulus value tothe Y tristimulus value, Z/Y, is a very useful parameter in definingspectral transmittance at the blue end of the spectrum, that is, in arange of 400-500 nm. Therefore, we have here used that ratio, ratherthan spectral purity, for describing our lens.

Currently, the CPF 450 filter lens is produced by firing a selected,photochromic glass lens in a hydrogen atmosphere for two hours at about476° C. The selected glass is designated as Code 8122. It has acomposition, as calculated in weight percent on an oxide basis, asfollows:

SiO₂ 56.3 Cl 0.22 B₂O₃ 18.1 Br 0.15 Al₂O₃ 6.2 Ag 0.21 K₂O 5.7 CuO 0.006TiO₂ 2.2 Er₂O₃ 0.25 Na₂O 4.1 Pd 0.0002 ZrO₂ 5.0 Li₂O 1.8

The Er₂O₃ and Pd contents are included to impart a fixed brown tint tothe lens. These colorants may be omitted if a clear, untinted glass isdesired. While the invention was developed using this glass, it is notso limited. For example, other available photochromic glasses may be sotreated.

One such glass, Code 8135, has the following composition, againpresented in weight percent on an oxide basis:

SiO₂ 56.4 Cl 0.215 B₂O₃ 18.1 Br 0.16 Al₂O₃ 6.2 Ag 0.24 ZrO₂ 5.0 CuO0.0057 TiO₂ 1.9 CoO 0.082 Na₂O 4.1 NiO 0.144 K₂O 5.7 LiO₂ 1.8

The colorant combination of CoO and NiO is included to provide a neutralgray tint to the lens. Again, this combination may be omitted if anuntinted glass is desired. Other known colorants may be included toprovide other fixed tints to a lens.

Protective, filter lenses are commonly produced by firing a suitablephotochromic glass lens in a flowing hydrogen atmosphere to provide athin reduced layer over the entire lens. While other reducingatmospheres may be employed, pure hydrogen has been found mosteffective. After the reduction treatment, the reduced layer on the frontsurface of the lens is removed to permit access of activating radiationto impart photochromic behavior. This is accomplished, for example, bygrinding and polishing the front surface of the lens.

It is a feature of the present invention that the need for thisoperation is obviated. Fortuitously, sufficient photochromic activatingradiation is transmitted through the reduced front surface of thepresent lens to avoid the need for front surfacing. Thus, the presentlens and process eliminate a time consuming and expensive, grinding andpolishing operation. This not only provides a significant cost savings,but broadens a product line to include progressive-type lenses.

FIG. 1 is a graphical representation in which wavelengths across thevisible spectrum are plotted in nm. on the horizontal axis, whiletransmittance in percent is plotted on the vertical axis.

Transmission curves for two lenses are shown in the FIGURE. Curve A isthe transmission curve for a current CPF 450 lens. Curve B is atransmission curve for a present lens, identified in TABLE I, infra, aslens 3.

It will be observed that, at wavelengths above about 460 nm, the twocurves are essentially the same. However, the lens prepared inaccordance with the present invention, lens 3, has markedly highertransmittance values in the 400-460 nm wavelength range than does thecurrent lens. This greater transmission in the blue end of the spectrumis a key virtue of the present invention.

Transmittances of the present lens are generally greater than 10%, butnot over about 30%, at any given wavelength in the 400-460 nm range. Incontrast, the transmittance values for the current CPF 450 lens aregenerally below 10% in this range.

SPECIFIC EMBODIMENTS

Polished, piano lenses having a nominal thickness of 2 mm. were preparedfrom both the Code 8122 and the Code 8135 photochromic glasses. Theselenses were fired in a flowing atmosphere of hydrogen gas in a tubefurnace for varying times and temperatures.

TABLE I, below, sets forth the glass, and the time and temperature ofthe firing cycle, for each lens tested. Firing time is given in minutes(min.), and temperature is given in °C.

TABLE I Glass Temp. (° C.) Time (min.) 1 Code 8122 476° 120 2 Code 8122485° 20 3 Code 8122 476° 8 4 Code 8135 476° 8

The visible-wavelength, spectral transmittances were measured. Thosedata were used to calculate tristimulus values by the weighted ordinatemethod using the 1931 CIE Standard Observer and Illuminant C. Data aregiven in the TABLE II below:

TABLE II Parameter 1 2 3 4 X 66.2 66.3 67.1 33.1 Y 73.6 73 71.6 36.9 Z14.8 15.8 22.8 13.3 x 0.4284 0.4276 0.4156 0.3971 y 0.4761 0.4703 0.44360.4433 Z/Y 0.201 0.217 0.318 0.361

FIG. 2 is a plot of the Z/Y ratio vs. spectral purity for several filterlenses calculated using Illuminant C. Also indicated is the Z/Y ratiofor Illuminant A (III. A) vs. the spectral purity found using theIlluminant C white point. The Z/Y ratio for Illuminant C (III. C) isabout 1.2, well outside the scope of FIG. 2, and not shown.

The present, inventive, filter lenses have Z/Y ratios similar to that ofIlluminant A, which is known to provide excellent color rendition. Webelieve that the excellent, color rendition performance of these lensesis a consequence of this close relationship.

When the chromacity coordinates of the inventive lenses are plotted on acolor mixture diagram, the dominant wavelength is found to be between570 and 580 nm. The range of preferred Z/Y ratios is 0.25-0.40.

The retina of the human eye has three types of cone photoreceptors thatprovide signals to produce color vision. These are designated S, M and Lcones indicating that they are more sensitive in the short, middle, orlong wavelength portion of the visible spectrum.

FIG. 3 is a graphical representation in which relative luminousefficiency is plotted on the vertical axis and wavelengths of thevisible spectrum are plotted in nanometers on the horizontal axis. Therelative luminous efficiencies for each type of cone photoreceptor areplotted against wavelengths. The resulting efficiency curve for eachcone type is designated by S, M, or L. A curve designated L+M gives theweighted efficiency sums for the L and M cones. (The ordinate scale waschosen to have the S and L+M curves peak at unity.) The weighted sum isused because the L and M cones are not present in equal numbers.

The y-bar and x-bar functions of the Standard Observer are used incalculating the Y and Z tristimulus values. When these y-bar and x-barfunctions are compared to data from FIG. 3, it is seen that the weightedsum represents the luminous efficiency function for photopic vision, andthat the z-bar and S luminous efficiency functions are the same. Thus,the ratio Z/Y relates the short wavelength-sensitive, cone stimulus tothe photopic stimulus.

The present invention provides inter alia,

1. A filter lens having filtering properties approximating those of theCPF 450 lens, but having surface coloration on both polished surfaces.This avoids a need to “front surface” a lens.

2. A lens that is similar in appearance to the CPF 450 product, but hashigher transmittance in the blue end of the spectrum. This provides amore natural scene.

3. A lens similar to the above made with a glass having a fixed tint.

4. A short time process for making lenses having these characteristics.

We claim:
 1. In an ophthalmic filter lens composed of anR₂O—Al₂O₃—B₂O₃—SiO₂ base glass containing photochromic constituents Ag,Cl, Br and CuO in small amounts sufficient to impart photochromicbehavior to the glass lens, the lens having polished surfaces which arereduced to provide a surface coloration that transmits sufficient activeradiation to activate the photochromic constituents, that has a ratio ofZ/Y tristimulus values between 0.25 and 0.40, that has a dominantwavelength between 570 and 580 nm on a color mixture diagram, that has asharp transmission drop between 500 and 460 nm, that has a transmissiongreater than 10%, but not over 30% between 400 and 460 nm, and thatprovides excellent color rendition.
 2. A progressive, ophthalmic filterlens in accordance with claim
 1. 3. A filter lens in accordance withclaim 1 wherein the lens is composed of a glass containing one or moreglass colorants to impart a fixed tint to the glass.
 4. A filter lens inaccordance with claim 1 wherein the lens is composed of an untintedglass.
 5. A filter lens in accordance with claim 1 wherein the lens hasa composition, calculated in weight percent on an oxide basis,consisting essentially of: 0-2.5% Li₂O, 0-9% Na₂O, 0-17% K₂O, 0-6% Cs₂O,8-20% Li₂O+Na₂O+K₂O+Cs₂O, 14-23% B₂O₃, 5-25% Al₂O₃, 0-25% P₂O₅, 20-65%SiO₂, 0.004-0.02% CuO, 0.15-0.3% Ag, 0.1-0.25% Cl, and 0.1-0.2% Br,wherein the molar ratio of alkali metal oxides:B₂O₃ varies between about0.55-0.85 and the weight ratio Ag:(Cl+Br) ranges between about0.65-0.95.